Generally, a cap part of snap button has a front surface defining a specific surface area, on which various kinds of designs may be selectively provided to achieve decorating and advertising effects.
In earlier stages, the required advertising and/or decorating design is formed on the front surface of the cap part of snap button by way of metal working or printing. However, the design so formed on the front surface of the cap part of snap button has poor quality and visual effect. In recent years, most cap parts of snap buttons are made with plastic material through injection molding. By way of multiple injections of different plastic materials, various designs may be formed on the front surface of the cap part of snap button. However, to enable multiple injections and distribution of plastic materials of different colors and properties at different stages, only non-closed designs may be formed on the front surface of the cap part of snap button. When it is desired to form a closed design, a relatively complicate mold assembly including multiple pieces of molds must be used in injection molding.
Taiwanese New Utility Model Patent published under No. 412944 discloses a cap part of snap button having a front surface design with a closed frame. According to the above-mentioned Taiwanese patent, a body portion of the cap part of snap button is first formed in a mold through injection molding, and then, a raised and closed frame is provided on a front surface of the molded body portion. Finally, a design portion having a color and properties different from that of the body portion is formed through a second injection molding, so that a cap part of snap button showing a design with a closed frame is formed. However, the following disadvantages are found in the process of molding the above-described cap part of snap button:    1. The half-finished product must be removed from the initial molds and correctly positioned at another place for a second time injection molding. The molding process is therefore troublesome.    2. The plastic materials for molding are subject to serious compression and deformation during the two injection molding processes. And, in the event all the differently colored plastic materials are soft plastics, it is difficult to complete the injection molding.    3. The second injection molding will encounter the problem of limited area of thrust surface.    4. The process could not be applied to a cap part of snap button including both closed and non-closed designs, such as a trademark device recognizing specific products.